A number of radioactive isotopes are present in cooling, operational and waste water from the daily operation of nuclear power plants and fuel rod holding tanks. While these radioactive isotopes are present in the water in very low concentrations, they are nonetheless highly radioactive and toxic to human life. Safe disposal or re-use of the contaminated water can only be conducted if a sufficient quantity of radioactive isotopes is removed to reach permissible levels.
The radioactive isotopes present in contaminated nuclear reactor water include cations and anions. The removal of radioactive cations using a porous glass cation exchanger is disclosed in my prior U.S. Pat. No. 4,469,628, entitled “Fixation By Ion Exchange of Toxic Materials In A Glass Matrix”. Similarly, the removal of radioactive anions using a porous glass or charcoal anion exchanger with a chelating agent, such as silver, is disclosed in my prior U.S. Pat. No. 4,659,477, entitled “Fixation of Anionic Materials With A Complexing Agent”.
Of particular interest, is the removal of radioactive anions, such as antimony (Sb), including antimony-125. Reactor waste waters have a pH close to neutral, which causes antimony to be present as a soluble anion. The removal of antimony must be accomplished in the presence of other non-radioactive anions, notably borate, which in the case of pressurized water reactors streams, is present at a concentration of about of 1000 ppm as dissolved boron. Over time, the concentration of dissolved boron can vary to be between 500 ppm to 1200 ppm of boron.
Current, attempts to remove radioactive antimony in this environment have been made using an anion exchange bed to remove the antimony in series with the other ion exchange beds presently being used to remove the other radioisotopes which are used to clean the waste water. While anion exchange beds can be effective for the removal of antimony, their cleaning capacity is generally limited to very low volumes, e.g., only 200 to 300 column-volumes, after which the antimony is re-released into solution, thus recontaminating the water. This is an unacceptable capacity, especially if one considers the disposal cost of the spent radioactive ion exchange material. Thus, the low capacity results in higher costs in the form of man-hours and disposal capacity of the used anion exchange material.
The waste processing plant of the Comanche Peak Nuclear Power Plant (Glen Rose, Tex.) has spent a substantial amount of time and resources in an effort to increase the capacity of its anion exchange beds to remove antimony-125 in particular. Unfortunately, it has failed in this effort.
Accordingly, it is an object of the present invention to overcome the shortcoming of the prior art by providing a method and apparatus to remove antimony and other hazardous and/or radioactive anions from reactor waste streams with a much higher capacity than that achieved with techniques currently employed in the industry.
These and other objects will become apparent from the foregoing description.